1. Field of the Invention
The present invention relates to a liquid detecting apparatus which constitutes a viscometer or density meter for detecting density of a measuring liquid, and more particularly to a liquid detecting apparatus in which a vibrating element composed of a piezoelectric vibrating plate is used as a vibrating source.
2. Related Art
Patent documents 1 and 2 disclose a liquid detecting apparatus comprising a liquid detecting element located at a lower end of a vibration shaft and immersed in a measuring liquid and a vibrating element located at an upper end of the vibration shaft and for vibrating the vibration shaft in a circular direction about the axis of the vibration shaft, wherein a piezoelectric vibrating plate capable of conducting a bending vibration is used as the vibration detecting element and the vibration shaft is vibrated in the circular direction by the bending vibration of the piezoelectric vibrating plate, thereby vibrating the liquid detecting element in the circular direction in the measuring liquid.
In the liquid detecting apparatus as represented by the above patent documents 1 and 2, the inner end edges of the respective piezoelectric vibrating plates are rigidly connected to the vibration shaft on their generating line, and a massive body is rigidly connected to the upper vibrating end on the opposite side of the liquid detecting element of each piezoelectric vibrating plate and the upper end of the vibration shaft, so that vibrations of the liquid detecting element are caused to occur in the circular direction in the measuring liquid by bending vibration of the lower vibrating end on the liquid detecting element side. Since each piezoelectric vibrating plate is rigidly connected at two sides along its upper vibrating end and inner end edge to the massive body and the vibration shaft, respectively, energy for transmitting vibration to the vibration shaft is reduced. As a result, energy for transmitting vibration to the liquid detecting element is reduced, thereby reducing the active vibration in the circular direction in the measuring liquid.
In addition, since the massive body, the vibrating plate and the vibration shaft are coaxially arranged in series, the overall length of the vibration unit becomes unduly large.
[Patent Document 1]
Official gazette of Japanese Patent Application Laid-Open No. H08-247917
[Patent Document 2]
Official gazette of Japanese Patent Application Laid-Open No. H08-86733